Digital three-dimensional manufacturing, also known as digital additive manufacturing, is a process of making a three-dimensional solid object of virtually any shape from a digital model. Three-dimensional object printing is an additive process in which one or more extruder or ejector assemblies form successive layers of material, for example thermoplastics such as acrylonitrile butadiene styrene (“ABS”) or polylactic acid (“PLA”), on a substrate in different shapes. In some conventional three-dimensional object printers, the extruders are similar to printheads in document printers. Such extruders include an array of extruders that emit a continuous stream of material to form layers, rather than an array of ejectors that eject drops of material.
In other known three-dimensional object printers, the extruder assembly includes a single nozzle configured to extrude the build material to form layers for production of a printed object. The nozzle is generally configured as a small circular hole that emits a continuous filament of build material. The filaments are laid down in adjacent strips layer by layer to form the three-dimensional part.
In such an extruder assembly, the printed object should be formed quickly and accurately. The size of the nozzle determines both the minimum resolution of the part and the speed at which the object can be formed. An extruder having a larger nozzle can form the object more quickly, but the resolution is reduced since the formation of the adjacent strips requires that the width of a layer be equal to an integer multiple of the nozzle width. An extruder having a smaller diameter nozzle, on the other hand, can be used to form smaller details, but, since the volume extruded in each pass is small the product requires more time to produce, sometimes on the order of hours or days. Thus, in conventional three-dimensional object printers, the size of the nozzle presents a trade-off between build speed and build resolution.
One solution to this problem is to use an extruder assembly having a large nozzle for larger objects and a small nozzle for detail formation. However, such an extrusion assembly is expensive since connections, valves, and control circuitry are required for each of the nozzles. Another solution has been to build parts that are mostly hollow inside using small nozzle extruder assemblies. While building hollow parts reduces the time necessary to produce the object, the structural strength of the object is severely reduced, limiting the utility of the hollow object.
Accordingly, improvements in systems and methods for forming three-dimensional objects with printers that include extruder assemblies so the objects have greater detail, increased structural strength, and reduced production time would be beneficial.